The present invention relates to a structure of a wiring board (or a circuit board), a producing method thereof, a semiconductor device, a producing method thereof, which are used in common electronic apparatuses each comprising a board(s) carrying an LSI(s), and an electronic apparatus, especially the same as above and a semiconductor device package structure which are suitable for such electronic apparatuses which are required to meet the compatibility between high reliability and a lower manufacturing cost.
Such a conventional wiring board can be seen in JP-A-62-263661.
According to the prior art, the multi-layered metal structure of which layers are interconnected with one another on a board and which comprises a bond layer comprising an element selected from the group of Ti, Ba, Cr and Ta, which is deposited on the board, a stress relaxation layer comprising an element selected from the group of Cu, Fe, Al, Ag, Ni and Au, which is deposited on the bond layer, a barrier layer comprising Ti or Zr and a wetable surface layer.
In the case where a solder is brought into direct contact with a wiring layer in order to connect a wiring board with an outer circuit, there will occur a phenomenon that composition elements of the solder and the wiring layer migrate each other between them during soldering or by a change with the passage of time after soldering resulting in loss of component elements of a wiring material (so called “solder damage”). Since an alloy layer is produced from the elements derived from the solder and the wiring layer under the phenomenon, there will arise a problem of harmful effects that the bonding part becomes brittle and of high electric resistance. If the “solder damage” further develops, the solder reaches the bottom face of the wiring material to deteriorate adhesion between the wiring material and an under layer so that the bonding part is delaminated from the under layer resulting in a defective product.
Therefore, in order to prevent occurrence of the above defect at the bending portion by soldering, the following two countermeasures have been usually adopted.
One method thereof is to prevent the solder from reaching the bottom face of the wiring material during the producing method and operation of the apparatus by making the wiring material thick.
Another method is to protect the wiring from the solder by providing a protective coating onto the wiring, which has high resistance against the solder damage, and by stopping the migration due to the solder within the protective coating.
The former method of making the wiring material thick does not solve the problem of strength reduction due to the formation of the alloy layer produced at the bonding part and causes some technical difficulties in other processes including a process of forming an insulation layer and another forming process because of an increase of the thickness of the wiring material.
In case of forming the protective coating layer with high resistance against the solder, namely the solder diffusion barrier layer called the UBM (Under Bump Material) or BLM (Ball Limiting Metallurgy) according to the latter method, a metal layer which is not usually used for wiring materials, for example, Ni, Ni—Cr, Ni—Cu, Pt, etc. must be additionally formed and processed so that the process steps increase and a higher level technology will be required.
On the other hand, because of demands for higher performance and more multi-function of electronic apparatuses, the total length of the wiring to be accommodated in the wiring board used for them is rapidly increasing so that the wiring becomes further finer and a further advanced multi-layer is required. Furthermore, in view of transfer quality of signals in a wiring board, requirements for the form of wiring and the positional accuracy of wiring, etc. become more strict and severer so that, for keeping the function at connecting portions with outside as stated in the above, it becomes difficult to change specifications for wiring. Therefore, in case of advanced electronic apparatuses, specifications for wiring are determined on the basis of electrical characteristics so that a structure, in which connecting electrodes with a material having higher resistance against the solder damage are provided to another layer, is becoming the main current.
But, such a structure has a problem that process steps increase and a higher level technology is required leading to a remarkably higher production cost.
Further, with regard to the fine wiring on wiring boards hereafter, it will be necessary to apply soldering to a wiring board with solder-connecting electrodes each having a small surface area, which is called “micro-soldering”. Especially, for a metal composition and a thickness of the UBM and forming thereof, a much higher level technology will be required in the future.